JPH02143137A - Method for evaluating life of heat resisting steel - Google Patents

Abstract

PURPOSE:To easily decide whether the holes formed between the grain boundaries of the metal of an object to be inspected exceed a life consumption region or not with high accuracy by measuring the above-mentioned holes with lapse of the service time and previously collating the holes with a predetermined master curve when the formed holes expand. CONSTITUTION:The ordinate of the master curve for predicting the material life in the case of evaluating the life of a heat resisting steel, such as CrMoV steel, indicates the peripheral length of the holes formed between the grain boundaries of the metal and the grain boundary width and the absissa indicates the life consumption, respectively. The results of the analyses to make image processing of the holes formed between the grain boundaries of the object to be inspected are drawn by a replica method in this detection method and are plotted. The holes gather at a point A and a point B if the service time is relatively short. The holes transfer and progress to a point C and a point D beyond the material life threshold line (the broken line of a vertical line) when the service life is long. The sizes of the holes 1a, 1b, 1c grow as the service time passes by in the beginning of the measurement. The holes connect to each other between the grain boundaries and expand like the width W.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for evaluating the fate of heat-resistant steel such as CrMOV steel.

(Prior art) For example, casings, steam valves, etc. applied to steam turbine equipment are exposed to high-temperature, high-pressure steam and operated for long periods of time, so it is necessary to thoroughly check their quality assurance. be. For the casing and the like, heat-resistant steel, such as CrMOV steel, is selected in consideration of the fact that it will be exposed to high-temperature and high-pressure steam, but even so, the strength of the material deteriorates due to long-term operation.

Conventionally, as a check method for quality assurance, color checkers, TA-type flaw detectors, and
Non-destructive testing methods such as ultrasonic inspection are applied to detect material defects in advance.

However, with such conventional methods, it is not possible to detect minute points of material deterioration, and for this reason, recently, a polarization measurement method that applies a voltage to the measurement site and predicts the R life of the material from the change value, and a method that applies an image to the measurement site. We are seeing the emergence of a so-called replica measurement method that predicts the lifespan of a material from changes in the metallographic structure that occur in the transferred source.

(Problem to be solved by the invention) However, although the former method and the latter method are much more accurate than conventional methods in checking the quality assurance of materials, Depending on the situation, there may be some discrepancies in the data, which may cause concerns about quality assurance, or in other words, predicting material life. This is because, in this type of field, it is known that the grain boundaries of metal crystals show vacancies as a result of long-term use. This is because predictions were only made by looking at trends, and were not meant to quantitatively grasp material life.

In view of the problem that conventional material life prediction is only a guideline, this invention provides a life evaluation method for heat-resistant steel that quantitatively understands material deterioration and enables accurate material life prediction. The purpose is to disclose.

[Structure of the invention]

(Means for Solving Problem A1) In order to achieve the above-mentioned object, the present invention measures the vacancies generated between the metal grain boundaries of the specimen as time passes, and If the pores generated between the holes expand, they are compared with a predetermined master curve to confirm whether or not they exceed the life consumption region determined by the master curve.

(Function) The inventor of this invention discovered that heat-resistant steel, which is exposed to high-temperature and high-pressure steam, has pores that are generated between metal grain boundaries in the specimen depending on the length of use. We focused on the fact that the difference between The size of the pores generated between the metal grain boundaries of the measured object is compared with the master curve created in By doing this, the accuracy of material life prediction will be increased.

(Example) Life evaluation of heat-resistant steel according to the present invention will be explained with reference to the drawings.

The embodiment described below is an example of CrM○■ steel used for a steam valve applied to a steam turbine device.

Figure 1 is a master curve for predicting material life.
The vertical axis shows the circumferential length and grain boundary width of pores generated between metal grain boundaries, and the horizontal axis shows the life consumption. The detection method is, for example, a replica method.

In Figure 1, the analysis results of the vacancies generated between the grain boundaries of the specimen are plotted by image processing.If the usage time is relatively short, the vacancies will gather at point △1 point B; It was detected that as the time became longer, the material life limit line (broken line on the vertical axis) was exceeded and the process moved to point C1.

As shown in Figures 2 and 3, the plot points shift from point A to point B and point C in order, as shown in Figures 2 and 3. Hole 1a,
It is thought that lb and lc grow in size as the usage time progresses, and the vacancies become connected between grain boundaries and the width W between the grain boundaries expands as shown in the third diagram. This is because it will be done.

This master curve was created based on a lot of empirical data and experimental data, and the left side of the vertical axis broken line is the life consumption residual area, and the right side is the life consumption danger area. The accuracy is higher than that of the conventional method of predicting material life.

Therefore, if the measured data of the object is plotted on a master curve and its position is within the area of points C and B shown in the first diagram, it can still be used sufficiently, and conversely, if it is within the area of point C1 shown in the first diagram, it can be used sufficiently. If so, it can be easily determined that the material itself must be replaced.

By comparing the actual data with the predetermined master curve in this way, it becomes possible to easily evaluate the prediction of the material life, and it is also possible to predict the future operating time of the actual machine.

〔Effect of the invention〕

As is clear from the above explanation, the life evaluation method for heat-resistant steel according to the present invention predicts material life by comparing actual data with a master curve, making it easier to predict material life than in the past. Moreover, it has the effect of being able to perform the process with high precision.

[Brief explanation of the drawing]

Fig. 1 is a master curve showing the correlation between the circumferential length of pores, the grain boundary width, and the material life consumption when predicting the life of a material; for example, the life curve of CrMOV steel; FIG. 2 is a diagram showing vacancies generated between grain boundaries, and FIG. 3 is a behavior diagram of vacancies showing the progress of vacancy growth. la, lb, 1cm...Vacancy W...Grain boundary width Agent Patent attorney Nori Chikaso Yudo Daishimaru Kugimi Kaisei★ (Vtr)

Claims (1)

[Claims] The vacancies generated between the metal grain boundaries of the specimen are measured over time, and if the pores generated between the metal grain boundaries expand, a predetermined master curve is determined. A life evaluation method for heat-resistant steel that checks whether the life consumption range determined by the master curve is exceeded.